Christchurch Wastewater Treatment Plant update

Friday 17 April 

Spikes of odour 

We're seeing a dip in the performance of the temporary activated sludge plant. Oxygen levels are lower than they should be, solids are building up, and the sludge is not settling as well as usual. This makes the system less stable and has resulted in an increase in stench around the plant, which can be seen on our hydrogen sulphide monitors. You can see this on our odour status map below, with the treatment plant moving from orange to red. 

As we move into cooler weather, these conditions increase the risk of odours coming from the ponds, especially if the amount of wastewater going into Pond 1 is not carefully controlled.

The operations team is making adjustments to improve plant performance. We are also looking at options to better spread flows across the ponds to reduce risk. Conditions are being closely monitored by our team who are ready to respond as needed. 

The good news is the ponds remain stable. Our monitoring has shown improvements in Pond 2a, which has shifted from orange to green on our odour status map. 

Mecca Place monitor offline this weekend

The hydrogen sulphide monitor on Mecca Place will be offline from this afternoon until Wednesday while some work takes place on the property where it is located.

What to expect this weekend

While the performance of the plant is reduced there's an ongoing risk of odour. It's possible there will be spikes of odour over the weekend, but as mentioned, our team are doing all they can to make adjustments to improve its performance. 

Website update: seasonal changes explained 

Odour at the Christchurch Wastewater Treatment Plant doesn’t stay the same all year. It follows a seasonal cycle driven by temperature, sunlight and biology in the ponds.

Summer and winter are generally the most stable periods. Odour is more likely during the change between seasons.

Head to our website to explore the graphic below and learn what factors influence odour throughout the year. 

Chemical trial starting in May 

Preparations are underway for a second odour control chemical trial at the plant, which will start in early May. The trial will assess products from multiple suppliers under the same operating conditions to ensure a consistent and comparable approach. The image above is from the first trial last year. 

At this stage, two suppliers have confirmed their intent to participate. Final participation will depend on suppliers confirming dosing requirements, and delivering product samples by the end of April.

The trial is expected to run for up to four months, after which results will be reviewed to inform next steps. We'll share further updates as the trial progresses.

Stay updated

We want everyone to be able to stay updated on what's happening at the Christchurch Wastewater Treatment Plant, and we regularly post new information on ccc.govt.nz/wastewaterfire 

You're welcome to send this update to your networks. If you know someone in the community who doesn’t have email or internet access, please print this newsletter off and pass it to them.

If you know of anyone who would like to receive this e-newsletter they can subscribe online. 

If you have any questions, or would like further information on the project, please call us on 03 941 8999 or 0800 800 169 or email wastewater@ccc.govt.nz  

Thanks for your patience and understanding. We’ll be in touch again soon.